The present invention relates to vacuum pumps and in particular to "hybrid" or compound vacuum pumps which have two or more sections of different operational mode for improving the operating range of pressures and throughput.
In European Patent Publication No. 0 805 275, for example, there is described a compound vacuum pump which consists of a regenerative section combined with a molecular drag section.
In European Patent Publication No. 0 643 227 there is described a compound vacuum pump having a turbo-molecular section and a molecular drag section.
A disadvantage of known compound vacuum pumps is that they tend to be bulky and there remains a need to improve compound vacuum pumps to increase efficiency whilst maintaining overall dimensions as small as is practicable.
It is an aim of the present invention to provide a compound vacuum pump having a turbo-molecular section and at least a molecular drag section which makes very efficient use of space when mounting the sections together.